What I've figured out so far is that you can buy "gambling" coins from jichan and when you can use them before beginning a game. Each coin multiplies the points you get, for ex if you score 10 0000 with one coin you'll get 20 0000. However using the coins is risky because if you score 10 0000 and you lose you will lose 20 000 yen from the money you earned. If you don't use the gambling coins  you'll just lose the points the yen you earned won't decrease. You can also buy tickets. With tickets you can double the score of each game and in case you lose you won't lose your yen.